1. Field of the Invention
The subject invention relates to an apparatus for calibrating the tension exerted on the strings of tennis rackets by stringing machines, and, in particular, an apparatus which accurately and reliably indicates the amount of tension which is exerted by the stringing machines.
2. Description of Related Art
For years tennis rackets were made of wood laminates. Today, wood rackets have, for the most part, been replaced by molded plastic frames.
Parallel with the development of these plastic frames comes a new sophistication in the manufacture of synthetic strings. The early mono-filament string, fashioned on a single strand of extruded nylon, is used only in the least expensive rackets. New technology has produced multifiber strings, both coreless and cored, that, in conjunction with the new rackets, offer a feel closely related to that of "gut". Most touring professional players still use gut strings. Gut, made from animal intestines, while being more expensive and less durable, offers more sensitivity, power and control to the player. Manufacturers try to emulate these qualities with their plastic strings while retaining the inherent advantages of synthetics, namely durability. It should be noted that 85% of the amateur players in the U.S. use synthetic strings.
Today, more so than ever, the combination of correct stringing tension and racket frame are critical to the playability of a racket. Manufacturers suggest a range of stringing tension for each racket they produce. Tighter stringing produces less power while giving greater control. Conversely, looser stringing produces more power and feel while exhibiting less control. In calculating the string tension best suited for ones own game, the player must consider the racket, power-play vs. control, court surface, etc.
Stringing a tennis racket involves bracing the racket in a frame holder to prevent the racket from distorting when it is subjected to extreme tensions. The string is woven into the racket using pre-formed holes along the side of the frame. The pattern of weaving is suggested by the racket manufacturer considering, among other things, how best to apply pressure to the strings without damaging or distorting the racket. In general, the end of the string is tied to the racket and the loose end is threaded through an appropriate opposing hole and then placed in a tension head, a vice-like device which pulls the string, either manually, electrically or pneumatically, to a predetermined tension. The string is then "clamped off" to maintain the tension and the loose end is woven further into the racket, again placed into the tension head where the same predetermined tension is applied to the length of string up to the clamp. The string is again clamped off and the process is repeated until all of the main strings and the cross strings are taut.
It should be apparent that there is a need for accuracy in setting the tension head prior to stringing; else the delicate combination of racket, string, player preference would be severely compromised. Before stringing, the tension head is set to the tension chosen by the player.
While there exists devices for checking the tension on tennis racket stringing machines, for example the EAGNAS TCG-100, these devices ordinarily consist of a tension spring with a marker attached thereto which indicates the applied tension on a scale inscribed on the housing. While the accuracy of these devices are sufficient for calibrating machines used for stringing rackets for beginners and some intermediate amateur players, with respect to upper intermediate and advanced amateur and professional players, the attainable accuracy with these devices is sorely lacking. It should be noted that a professional player can easily notice the inconsistency of one pound of tension!